Most optometric and ophthalmic procedures, such as retinal examinations, tonometry and eye surgery, require accurate aligning of the instrument being used in them.
Known alignment methods are usually based on illumination of the eye followed by detecting the back-scattered light or by imaging the eye. AU patent 2006246323B2 is an example of the former solution and JP patents 0330841662 and 050245262, EP patent 254002B1 and CN patent 102551654 of the latter one.
Some alignment methods are meant to be performed either by the patient himself or as a result of feedback information from the patient. Such self-alignment methods are especially used in hand-held tonometers for measuring eye-pressure, for which EP
Even these self-alignment methods, however, are based on imaging the eye, and they are not user-friendly enough to be used in instruments for home use.
U.S. Pat. No. 5,442,412 discloses a patient responsive eye fixation target method. The device to perform the method is based on a sensor that detects eye movement and notifies the patient of an erroneous eye position with a requirement to change it. The device has two light sources that produce a dot and a circle, respectively, to be seen by the patient for helping the patient to return the correct eye position. The device supplies an eye movement error signal to one of the second light sources to adjust the dot's appearance for guiding the patient in the realignment.
This quite complicated solution is intended for a great variety of ophthalmic procedures, laser surgery included.
There is therefore a need for a simple alignment method that reliably could be performed by the patient himself with instruments for home use without problems.